Wafer handling system and method for use in lithography patterning

ABSTRACT

The present invention includes a lithography system comprising a lithography patterning chamber, a wafer exchange chamber separated from the lithography patterning chamber by a first gate valve, and at least one alignment load-lock separated from the wafer exchange chamber by a second gate valve. The alignment load-lock includes an alignment stage that aligns a wafer during pump-down. An alignment load-lock according to the present invention can be uni-directional or bi-directional. Likewise, a lithography system according to the present invention can include one or multiple alignment load-locks. Also disclosed is a method of patterning a wafer within a lithography system. The method can include a first step of placing the wafer on supports within an alignment load-lock. In a next step, the wafer is aligned with respect to a chuck while the wafer is supported within the alignment load-lock on the supports. In another step, the wafer is secured to the chuck. And in yet another step, pump-down is performed to create a vacuum within the alignment load-lock.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a wafer handling system andmethod for use within a lithography system. More particularly, thisinvention relates to a system and method of wafer handling in whichwafers are transported within a lithography system while being affixedand aligned to chucks, thereby maximizing production throughput.

[0003] 2. Related Art

[0004] Lithography is a process used to create features on the surfaceof substrates. Such substrates can include those used in the manufactureof flat panel displays, circuit boards, various integrated circuits, andthe like. A frequently used substrate for such applications is asemiconductor wafer. While this description is written in terms of asemiconductor wafer for illustrative purposes, one skilled in the artwould recognize that this description also applies to other types ofsubstrates known to those skilled in the art. During lithography, awafer, which is disposed on a wafer stage, is exposed to an imageprojected onto the surface of the wafer by exposure optics locatedwithin a lithography apparatus. While exposure optics are used in thecase of photolithography, a different type of exposure apparatus may beused depending on the particular application. For example, x-ray, ion,electron, or photon lithographies each may require a different exposureapparatus, as is known to those skilled in the art. The particularexample of photolithography is discussed here for illustrative purposesonly.

[0005] The projected image produces changes in the characteristics of alayer, for example photoresist, deposited on the surface of the wafer.These changes correspond to the features projected onto the wafer duringexposure. Subsequent to exposure, the layer can be etched to produce apatterned layer. The pattern corresponds to those features projectedonto the wafer during exposure. This patterned layer is then used toremove exposed portions of underlying structural layers within thewafer, such as conductive, semiconductive, or insulative layers. Thisprocess is then repeated, together with other steps, until the desiredfeatures have been formed on the surface of the wafer.

[0006] Step-and-scan technology works in conjunction with a projectionoptics system that has a narrow imaging slot. Rather than expose theentire wafer at one time, individual fields are scanned onto the waferone at a time. This is done by moving the wafer and reticlesimultaneously such that the imaging slot is moved across the fieldduring the scan. The wafer stage must then be stepped between fieldexposures to allow multiple copies of the reticle pattern to be exposedover the wafer surface. In this manner, the sharpness of the imageprojected onto the wafer is maximized. Through increases in bothalignment precision and projection accuracy, today's lithography toolsare capable of producing devices with ever decreasing minimum featuresize. However, minimum feature size is but one measure of a lithographytool's utility. Another critical measure is throughput.

[0007] Throughput refers to the number of wafers per hour that can bepatterned by a lithography system. Every task that must be performed onwafers within a lithography system contributes to the total timerequired to pattern the wafers, with an associated decrease inthroughput. One critical task that must be performed repeatedly within alithography system is wafer alignment. Wafers must be precisely alignedwithin a lithography system in order to achieve high levels of overlayaccuracy. Unfortunately, alignment precision is usually lost wheneverwafers are moved within conventional lithography systems with robots.

[0008] What is needed is a system and method for handling wafers withina lithography system that both avoids the loss of alignment caused byconventional robots, while at the same time improving system throughput.

SUMMARY OF THE INVENTION

[0009] In one embodiment, the present invention includes a lithographysystem having a lithography patterning chamber, a wafer exchange chamberseparated from the lithography patterning chamber by a first gate valve,and at least one alignment load-lock separated from the wafer exchangechamber by a second gate valve. The alignment load-lock includes analignment stage that aligns a wafer during pump-down. An alignmentload-lock according to the present invention can be uni-directional orbi-directional. Likewise, a lithography system according to the presentinvention can include one or multiple alignment load-locks.

[0010] A lithography system according to the present invention can alsoinclude a holding load-lock separated from the wafer exchange chamber.

[0011] A lithography system according to the present invention canfurther include an illumination source that emits light having aninspection wavelength, and a camera sensitive to said inspectionwavelength. A roof of the alignment load-lock is transparent to theinspection wavelength to allow observation of the wafer contained withinthe alignment load-lock.

[0012] Also included within the alignment load lock according to anembodiment of the present invention are supports for holding a wafer.These supports can be hooks, pins, and the like. An alignment stage isfurther located within the alignment load lock. The alignment stage isseparated from an alignment sub-stage disposed outside of the alignmentload-lock by a column extending through a floor of the alignmentload-lock. Furthermore, the floor of the alignment load-lock can includea motion feedthrough seal that allows the column to move relative to thefloor while preventing gas flow into the alignment load-lock. Such amotion feedthrough seal can include bellows and rotary seals such asferromagnetic seals.

[0013] Further included in an embodiment of the present invention aremultiple chucks. The chucks can be electrostatic chucks or vacuumchucks. The chucks can include cutouts for accommodating the wafersupports within the alignment load-lock. The chucks can further includechuck engagement mechanisms for kinematically mounting the chucks to thealignment stage or to a stage located within the lithographypatterninging chamber. In critical areas, the chuck engagementmechanisms can be kinematic hemispheres in order to avoid stress andstrain, including, for example, hemispheres for engagement withvee-blocks located on the various stages within the lithography system.

[0014] In an embodiment of the present invention, the lithographypatterninging chamber can include multiple exposure stages.

[0015] Also disclosed is a method of patterning a wafer within alithography system. In an embodiment, the method includes a first stepof placing the wafer on supports within an alignment load-lock. In anext step, the wafer is aligned with respect to a chuck while the waferis supported within the alignment load-lock on the supports. In anotherstep, the wafer is secured to the chuck. And in yet another step,pump-down is performed to create a vacuum within the alignmentload-lock.

[0016] In a method according to the present invention, pump-down can beperformed concurrently with aligning the wafer relative to the chuck.Likewise, pump-down can be performed concurrently with securing thewafer to the chuck subsequent to the alignment step.

[0017] A method according to an embodiment of the present invention canalso include a step of transporting the chuck and wafer to a lithographypatterning chamber. Further fine alignment may be needed in thelithography patterning chamber. Next, a step of performing lithographypatterning on the wafer is conducted. Once the lithography patterning iscomplete, the wafer and chuck are returned to the alignment load-lockarea. Once back at the alignment load-lock, the chuck can be removedfrom the wafer and venting can be performed. The venting can take placewhile the wafer is being removed from the chuck.

[0018] Also disclosed herein is a method of aligning a wafer within analignment load-lock. In an embodiment, this method includes a first stepof placing the wafer on supports within the alignment load-lock. Next, astep of observing the location and orientation of the wafer on thesupports within the alignment load-lock is performed. Also performed isa step of moving a chuck so as to align the wafer with respect to thechuck. Once aligned, the chuck is then placed in contact with, andsecured to, the wafer. The step of observing the location andorientation of the wafer can be performed by a camera located outside ofthe alignment load-lock.

BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying drawings, which are incorporated herein and formpart of the specification, are illustrations of the present inventionand, together with the description, further serve to explain theprinciples of the invention and to enable a person skilled in thepertinent art to make and use the invention. Like reference numbersrefer to like elements within the different FIG.s.

[0020]FIG. 1 is an illustration of a lithography system according to thepresent invention.

[0021]FIG. 2A is an exploded view of the upper elements within analignment load-lock according to the present invention.

[0022]FIG. 2B is an exploded view of the lower elements within analignment load-lock according to the present invention.

[0023]FIG. 3A is an illustration of a floor-mounted motion feedthrough300 within a lithography system according to the present invention.

[0024]FIG. 3B is an illustration of a wall-mounted motion feedthrough350 within a lithography system according to the present invention.

[0025]FIG. 4A is an illustration of a method of patterning a waferwithin a lithography system utilizing a bidirectional load-lock(s)according to the present invention.

[0026]FIG. 4B is an illustration of a method of patterning a waferwithin a lithography system utilizing a unidirectional load-lock(s)according to the present invention.

[0027]FIG. 5 is an illustration of a method of aligning a wafer withinan alignment load-lock according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] As used herein, the term wafer means a semiconductor wafer, orany other substrate suitable for lithographic patterning.

[0029] Alignment, pump-down, and charging of an electrostatic chuck areall procedures that take up precious time within a lithographypatterning process. The present inventors have discovered that all threeof these functions can be combined into a single alignment load-lockstation. Such a single alignment load-lock station can align a waferwith respect to a chuck and then secure that wafer to the chuck, all thewhile pumping-down the load-lock. By including more than one chuckwithin such a lithography system, wafers can be secured to theirrespective chucks during lithography patterning, thereby maximizingthroughput.

[0030]FIG. 1 is an illustration of a lithography system 100 according tothe present invention. Lithography system 100 patterns wafers, indicatedby dashed circles within the FIG., that are obtained from a track 101.Wafers obtained from track 101 have undergone various processes asrequired prior to lithography patterning. For example, resist-apply,pre-bake, and other processes known to those skilled in the relevantart(s) are conducted on wafers prior to lithography patterning. Afterlithography patterning, wafers are returned to the track for furtherprocessing steps, such as development, post bake, and the like. Track101 is connected to lithography system 100 via two gate valves 102, 103.Gate valves 102, 103 are of the type known to those skilled in therelevant art(s) as being capable of maintaining different atmosphericpressures on either side of the gate valve. Gate valves 102, 103separate track 101 from two alignment load-locks 104, 105.

[0031] Alignment load-locks 104, 105 are separated from a wafer exchangechamber 106 by gate valves 107, 108. Gate valves 107, 108 are analogousto gate valves 102, 103 that connect alignment load-locks 104, 105 tothe track 101. Each alignment load-lock 104, 105 is thus a chamberseparated from track 101 and wafer exchange chamber 106 by respectivegate valves. Alignment load-locks 104, 105 are further connected tovacuum and venting elements (not shown) that allow the alignmentload-locks to be transitioned from atmospheric pressure to vacuum(pumped-down) and back to atmospheric pressure again (vented). In thisway, wafer exchange chamber 106 can be held at a high vacuum while track101 is held at atmospheric pressure. Alignment load-locks 104, 105 thusserve to move wafers in and out of the wafer exchange chamber whiletransitioning from atmospheric pressure to high vacuum. The presentinventors have discovered that by including alignment and chuckingfeatures within alignment load-locks 104, 105, overall system throughputcan be greatly enhanced. Alignment load-locks 104, 105 will be discussedin greater detail below in connection with FIGS. 2a and 2 b.

[0032] Wafer exchange chamber 106 includes a robot 109 having a dualend-effector. Robot 109 is vacuum compatible and is capable of handlingtwo chucks at once by virtue of its dual end-effctor. Alternatively,other structures can be used to transport the chuck with aligned waferfrom the alignment load-lock to the lithography patterning chamber aswould apparent to those skilled in the relevant arts given thisdisclosure. For example, a robot having a single end-effector, or dual,non-robotic, transport mechanisms could also be used without departingfrom the scope of the present invention.

[0033] Wafer exchange chamber 106 is connected to lithography patterningchamber 111 by gate valve 110. Gate valve 110 is similar to the othergate valves described herein. Lithography patterning chamber 111includes wafer stages 112, 113. Wafer stages 112, 113 are capable ofmovement in the directions indicated for fine alignment and exposureprocesses. Lithography patterning chamber 111 thus further includesprojection optics or other elements necessary to perform the lithographypatterning. While lithography patterning chamber 111 includes two waferstages 112, 113 a lithography patterning chamber could also include onewafer stage. A dual wafer stage structure like that shown is describedin more detail in co-pending, commonly owned U.S. patent applicationSer. No. 09/449,630, titled “Dual-Stage Lithography Apparatus andMethod,” filed Nov. 30, 1999, which is hereby incorporated by referencein its entirety.

[0034] Lithography system 100 further includes a holding load-lock 114.Holding load-lock 114 is used to hold a spare chuck, or to exchangechucks within the lithography system while maintaining lithographypatterning. This allows access to a chuck held in holding load-lock forcleaning, for example. Holding load-lock 114 also includes gate valves115 and 116. While the presence of holding load-lock is preferable, asit allows chuck exchange without stopping lithography patterning, it canbe omitted without departing from the scope of the present invention.

[0035] While alignment load-locks 104, 105, and holding load-lock 114are all preferably bi-directional load-locks, uni-directional load-lockscould also be used without departing from the scope of the presentinvention. Unidirectional load-locks are capable of wafer input or waferoutput only. Bidirectional load-locks, however, are capable of bothwafer input and wafer output.

[0036] For example, if the wafer is transferred from track 101 to aunidirectional alignment load-lock and then to patterning chamber 111,it cannot then be transferred to the same unidirectional alignmentload-lock after it has been patterned. Rather, after the patterningprocess is completed in the lithography patterning chamber, the wafermust instead be returned to another alignment load-lock and then, inturn, to track 101.

[0037] By contrast, if the wafer is transferred from track 101 to abidirectional alignment load-lock and then to lithography patterningchamber 111, after patterning, the wafer can be transferred back throughthe same bidirectional alignment load-lock to track 101.

[0038] While the use of two bi-directional alignment load-locks isadvantageous as it allows for greater system throughput, two singleunidirectional load-locks could also be used. Likewise, a singlebi-directional alignment load-lock could also be used without departingfrom the scope of the present invention. The precise structure andfunction of each of alignment load-locks 104, 105 will now be describedin connection with FIGS. 2A and 2B.

[0039]FIGS. 2A and 2B together constitute an exploded view of theelements within an alignment load-lock according to the presentinvention. FIG. 2A corresponds to the upper portion of an alignmentload-lock according to the present invention, while FIG. 2B correspondsto the lower portion of an alignment load-lock according to the presentinvention. The walls of the alignment load-lock are not shown in eitherof FIGS. 2A or 2B.

[0040] Alignment load-lock roof 201 is an airtight transparent orsemi-transparent window. A camera 202 and an illumination source 203 aredisposed above alignment load-lock roof 201. By “semi-transparent,” itis meant that alignment load-lock roof 201 is at least transparent to aninspection wavelength of light emitted from illumination source 203 towhich camera 202 is sensitive. Within the alignment load-lock are wafersupports 204, 205, 206. These wafer supports 204-206 are used to hold awafer 207. Wafer supports 204-206 are illustrated in the FIG. as hooks,but could also comprise pins, or other supporting mechanisms, as wouldbe apparent to one skilled in the relevant art(s). Wafer 207 has beenplaced on wafer supports 204-206 from track 101 by an additional robot,which is customarily part of the track system (not shown). Moreover,wafer 207 can undergo prior coarse alignment so that notch 208 or otherdesired feature is placed within a field of view 209 of the camera 202,which is within an illumination field 210 of the illumination source203. Such prior coarse alignment can be accomplished in a manner knownto those skilled in the relevant art(s). For example, it can beperformed by a module in the track that spins the wafer and locates thenotch using a photoelectric sensor. Also included within the alignmentload-lock shown is a chuck 211 having chuck cutouts 212, 213, and 214.Chuck cutouts 212-214 are large enough to accommodate a range of motionif the chuck such that wafer supports 204-206 can be accommodated withinthese chuck cutouts 212-214. Thus, chuck cutouts 212-214 line upapproximately with wafer supports 204-206.

[0041]FIG. 2B corresponds to the bottom portion of the alignmentload-lock. Specifically, alignment load-lock floor 216 having a motionfeedthrough seal 217 is located at a bottom portion of the alignmentload-lock. Motion feedthrough seal 217 allows movement of a column 230,upon which is disposed an alignment stage 218, with respect to theload-lock floor while preventing gas from flowing into the load lock. Inthe particular embodiment shown, motion feedthrough seal 217 comprisesbellows that will be described below in greater detail with respect toFIG. 3. Alternatively, other types of motion feedthrough seals, such asa movable seal or a ferrofluidic seal, could be used without departingfrom the scope of the present invention.

[0042] Alignment stage 218 include stage engagement mechanisms 219, 220,and 221. Stage engagement mechanisms are used for kinematically mountingthe chuck 211 with chuck engagement mechanisms 222-224 disposed on thelower surface of the chuck 211. In critical areas, the chuck engagementmechanisms can be kinematic hemispheres in order to avoid stress andstrain, including, for example, hemispheres for engagement withvee-blocks 219-221 located on the various stages within the lithographysystem. In the embodiment shown, stage engagement mechanisms 219-221comprise vee-blocks 219-221 that constitute the bottom half of akinematic mount. Likewise, in the embodiment shown, chuck engagementmechanisms 222-224 comprise hemispheres that constitute the top half ofthe kinematic mount. As would be apparent to one skilled in the relevantart(s) given this description, other types of kinematic mounts can beused without departing from the scope of the present invention.

[0043] In the embodiment shown, chuck 211 is an electrostatic chuckcapable of maintaining an electric charge sufficient to hold a wafer foran extended period of time. In one embodiment, however, chuck 211 is avacuum chuck. Alignment stage 218 further includes contact block 225,having pogo contacts 226 and 227. Pogo contacts 226, 227 are used tomake electrical contact with contact pads 228 and 229 disposed on thebottom of chuck 211. In one embodiment, pogo contacts 226 and 227 arespring-loaded contacts made of metal tubing. The metal tubing comprisesa spring with a metal bar. The metal bar contacts the contact pads 228and 229. Chuck 211 is charged and discharged through contact pads 228and 229 when connected to pogo contacts 226 and 227. While the presentinvention is described in terms of an electrostatic chuck, other chuckscan be used without departing from the scope of the present invention.For example, vacuum chucks, mechanical clamping, and other means ofsecuring a wafer to a chuck could be used, as would be apparent to oneskilled in the relevant art(s). Due to the high vacuum environment inwhich extreme ultraviolet light processing occurs, electrostatic chucksare preferable.

[0044] Alignment stage 218 is positioned at the top of column 230.Column 230 is disposed atop an alignment substage 231, which is held byan alignment substage mount 232. Additional motor and control elements(not shown) are used to move the alignment stage in four degrees offreedom (rotation, two horizontal translations, and a verticaltranslation) and as indicated by the arrows in the FIG., as would beapparent to a person skilled in the relevant art(s), given thisdescription. Motion feedthrough seal 217 serves to separate the highvacuum environment within the alignment load-lock from the alignmentsubstage 231, alignment substage mount 232, and the remainder of thelithography system.

[0045] Operation of the elements within the alignment load-lock will nowbe described. It should be noted that chuck 211 and wafer 207 are notintegral parts of the alignment load-lock. Rather, chuck 211 is one of anumber of like chucks which are used within the lithography system 100.Likewise, wafer 207 has been obtained from track 101 for lithographypatterning within lithography patterning chamber 111, of the systemshown in FIG. 1. As mentioned above, wafer 207 may have undergone coarsealignment prior to being placed on wafer supports 204-206. This coarsealignment can be performed in order to place notch 208 within the fieldof view 209 of camera 202. Since camera 202 can see notch 208, thecamera 202 can determine both the center of the wafer from the radius ofcurvature visible within the field of view 209 as well as theorientation of the wafer from the location of notch 208. In thisrespect, it should be noted that while one camera 202 has been shown inFIG. 2A, a plurality of such cameras and light sources 203 can be usedwithout departing from the scope of the present invention. Since camera202 is used for determining notch location 208 as well as the radius ofcurvature of wafer 206, the use of more than one camera can increase theprecision of the observations, as would be apparent to one skilled inthe relevant art(s) given this disclosure. Best results would beobtained with two diametrically opposed cameras (or equally spacedcameras, in reference to the wafer).

[0046] Camera 202 looks at field of view 209 to determine wafer location207. This wafer location is then output by camera 202 to a patternrecognition unit 233 (not shown). The pattern recognition unit sendslocation information to alignment substage 232. Since the patternrecognition unit knows the precise orientation and location of wafer 207it can control the location of alignment stage 218 through alignmentsubstage 231 and alignment substage mount 232. Once chuck 211 has beenaligned with wafer 207, chuck 211 is moved up to and put in contact withwafer 207. Once in contact with wafer 207, chuck 211 is charged throughcontact pads 228 and 229, which are in contact with pogo contacts 226and 227 at contact block 225 of alignment stage 218. Since chuck 211 hasbeen aligned with wafer 207 prior to chuck 211 being charged, wafer 207is firmly held in contact with chuck 211 by virtue of the charge. Sinceeach wafer stage 112, 113 within lithography patterning chamber 111includes kinematic mounts, the repeatability of chuck placement on waferstages 112, 113 within the lithography patterning chamber is limited tothe accuracy of the kinematic mounts. The kinematic mounts shown, whichuse vee-blocks and hemispheres, have a repeatability of about twomicrons. Since chuck 211 can maintain its electrostatic charge withinthe lithography system 100, the alignment of a wafer, for example, wafer207, will always be within the repeatability of the kinematic mountsused.

[0047] Returning to FIG. 1, it should be apparent from the abovediscussion in connection with FIGS. 2A and 2B that while a wafer iswithin either of alignment load-locks 104 or 105, alignment and chuckingoperations can be performed while the alignment load-lock is undergoingpump-down. Once a wafer within alignment load-lock 104 or alignmentload-lock 105 has been aligned with respect to a chuck and attached tothat chuck, and pumpdown is complete, the gate valve 107, or 108, can beopened, at which point robot 109 can lift the chuck and wafer togetherfrom within either alignment load-lock and move it to the lithographypatterning chamber 111. Since robot 109 includes a gripper, it can holdtwo chucks at once. Thus, robot 109 can swiftly exchange chucks betweeneither alignment load-lock station and either wafer stage.

[0048]FIG. 3A is an illustration of a floor-mounted motion feedthrough300 within a lithography system of the present invention. Bellows 302allow vertical and horizontal translations of shaft 230 relative toload-lock floor 216, while maintaining vacuum inside the load lock.Bellows 302 include a plurality of metal, preferably stainless steeldisks welded at their peripheral and inside edges. These bellows allowcolumn 230 to move in six degrees of freedom while maintaining a vacuumseal. Rotary seal 304 allows rotation of shaft 230, while maintaining avacuum. Bearing 306 captures shaft flange 308, preventing collapse ofthe bellows due to atmospheric pressure. It will be apparent to oneskilled in the art that seal 304 can be an elastomer seal, a pre-loadedteflon seal, or a ferrofluidic seal. It will also be apparent that thetransfer of rotary motion accomplished by 304-308 could have also beenaccomplished via a magnetic coupling.

[0049]FIG. 3B is an illustration of a wall-mounted motion feedthrough350 within a lithography system of the present invention. Bellows 352,attached to chamber wall 354, allows vertical and horizaontaltranslation of alignment stage 218. Bellows 352 also allow a limitedamount of rotation of alignment stage 218 about its centerline 356. Thisarrangement does not require a rotary seal, and is, therefore, lessleak-prone than the apparatus of FIG. 3A. However, whereas the rotaryseal 304 of FIG. 3A allows unlimited rotation, the bellows 352 onlyallow a few degrees of rotational freedom. The limited amount ofrotation is sufficient if a coarse alignment step is performed on thewafer (by the track) before introducing the wafer in the load-lock. Itwill be understood that a second wall-mounted feedthrough mechanismcould be added diametrically opposite to the one shown through a hole inan opposite wall in order to improve mechanical stability of theapparatus, without deviating from the present invention.

[0050]FIG. 4A is an illustration of a method 400 of patterning a waferwithin a lithography system utilizing at least one bidirectionalalignment load-lock according to the present invention. It should benoted that such a system can comprise only one bidirectional alignmentload-lock or a plurality of bidirectional alignment load-locks toincrease efficiency and throughput. In the embodiment utilizing abidirectional alignment load-lock system, unlike the embodimentutilizing a unidirectional alignment load-lock system, the bidirectionalalignment load-lock(s) is capable of accepting the wafer from track 101as it enters the lithography system (input) and also allowing the waferto enter it after patterning and be dispelled from it back to track 101(output). In other words, the wafer can be transferred from track 101 tothe bidirectional alignment load-lock, from the bidirectional alignmentload-lock to the patterning chamber, from the patterning chamber afterpatterning to the same bidirectional alignment load-lock, and then fromthe bidirectional alignment load-lock to the track 101.

[0051] In a first step 410 of the method 400 of FIG. 4A, a wafer isplaced on wafer supports within a bidirectional alignment load-lock(s).As described above in connection with FIG. 1, the wafer can be takenfrom a track before being placed onto supports within the bidirectionalalignment load-lock(s). Placing the wafer on the supports within thebidirectional alignment load-lock(s) can be accomplished with, forexample, a robot. As described above in connection with FIG. 2A, thewafer supports within the bidirectional alignment load-lock(s) cancomprise hooks, pins, and the like. Also, as described above inconnection with FIG. 1, the bidirectional alignment load-lock(s) cancomprise a conventional load-lock chamber with gate valves separating atrack from a wafer transport chamber. In a lithography system operatingat high vacuum, such a wafer transport chamber would be kept at highvacuum while the track would be kept at atmospheric pressure. Thebidirectional alignment load-lock(s) is thus used to transfer wafers inand out of the high vacuum environment within the lithography apparatusitself without exposing the entire apparatus to atmospheric pressure.

[0052] In a next step 420, the wafer is aligned with respect to a chuck.As described elsewhere herein, the chuck can be an electrostatic chuck,a vacuum chuck, or a chuck with other mechanical clamping features. In anext step 421, the aligned wafer is secured to the chuck. The securingof the aligned wafer to the chuck 421 can be accomplished by moving thechuck up to and in contact with the wafer and then, in the case of anelectrostatic chuck, charging the electrostatic chuck to thereby securethe wafer to the chuck. Such charging can be accomplished through theuse of pogo contacts on an alignment stage which are in contact withpads on the bottom surface of the electrostatic chuck. Further detailsof steps 420 and 421 are described in greater detail below in connectionwith FIG. 5.

[0053] In a step 425, concurrent with at least one or both of steps 420and 421, a pump-down is performed within the bidirectional alignmentload-lock(s). As is known to those skilled in the relevant art(s),pump-down is the procedure whereby the load-lock is evacuated of gasesthus bringing it from atmospheric pressure to high vacuum. As describedelsewhere herein, the present inventors have discovered that byperforming the pump-down operation simultaneously with the alignment ofthe wafer with respect to the chuck and the securing of the wafer to thechuck, greater throughput can be realized within a lithography systemaccording to the present invention.

[0054] In a next step 430, the chuck with the aligned wafer istransported to a lithography patterning chamber. As described above inconnection with FIG. 1, the transportation of the chuck from thebidirectional alignment load-lock(s) to the lithography patterningchamber can be accomplished by a robot located within a wafer exchangechamber disposed between the bidirectional alignment load-lock(s) andthe lithography patterning chamber. Such a robot can have a dual enddefector to realize greater efficiency of transportation of chucksbetween bidirectional alignment load-lock(s) and the lithographypatterning chamber. Alternatively, other structures can be used totransport the chuck with aligned wafer from the bidirectional alignmentload-lock(s) to the lithography patterning chamber, as would apparent tothose skilled in the relevant art(s) given this disclosure. Forinstance, the chuck and wafer could be placed on a kineumatic mount ofthe exposure stage.

[0055] Once the chuck with aligned wafer have been placed into thelithography patterning chamber, lithography patterning is performed in anext step 440. Such lithography patterning can include a final alignmentstep as well as additional steps used within lithography patterning asare known to those skilled in the relevant art(s).

[0056] In a next step 450, the chuck with processed wafer are removedfrom the kineumatic mount of the exposure stage to a bidirectionalalignment load-lock(s) from the lithography patterning chamber. Asdescribed above in connection with step 430, the transportation of thechuck with the processed wafer from the lithography patterning chamberto the bidirectional alignment load-lock(s) can be performed with arobot located within a wafer exchange chamber. Moreover, the chuck withpatterned wafer can be brought back to the same bidirectional alignmentload-lock(s) through which it entered the system.

[0057] In a next step 460, the processed wafer is removed from the chuckwithin the bidirectional alignment load-lock(s). This step issubstantially the reverse of process step 421, discussed above. Thus,once the chuck with patterned wafer is returned to the bidirectionalalignment load-lock(s), the chuck can be discharged. Once discharged,the chuck can be lowered away from the wafer leaving the wafer held bythe wafer supports. Concurrently with step 460, a venting operation isperformed at a concurrent step 465. Venting is the process by which thepressure within the bidirectional alignment load-lock(s) is brought fromhigh vacuum back to atmospheric pressure. As with steps 420, 421, and425, the venting step 465 is performed simultaneously with step 460. Aswith the pump-down process, performing venting while removing the waferfrom the chuck further increases the throughput of a lithography systemaccording to the present invention.

[0058] In a final step 470, the now patterned wafer is removed from thebidirectional alignment load-lock(s) and placed back onto the track.Alternatively, the wafer can be placed onto another structure used tomove wafers away from the lithography apparatus. As will be apparent toa person skilled in the relevant arts, after the final step 470 of themethod 400 of FIG. 4 has been performed, the lithography system has beenreturned to its condition existing prior to the first step, 410.Accordingly, method 400 can be repeated indefinitely for the lithographypatterning of multiple wafers.

[0059]FIG. 4B is an illustration of a method 472 of patterning a waferwithin a lithography system utilizing unidirectional alignmentload-lock(s) according to the present invention. In a first step 474 ofthe method 472 of FIG. 4B, a wafer is placed on wafer supports within aninput alignment load-lock. The input alignment load-lock isunidirectional, as the wafer does not exit the system through the samealignment load-lock through which it entered the system. Rather, it isreturned to another alignment load-lock (output alignment load-lock)after it undergoes patterning in the patterning chamber and exits thesystem (i.e., transferred to track 101) through the output alignmentload-lock. As described above in connection with FIG. 1, the wafer canbe taken from a track before being placed onto supports within the inputalignment load-lock. Placing the wafer on the supports within the inputalignment load-lock can be accomplished with, for example, a robot.

[0060] As described above in connection with FIG. 2A, the wafer supportswithin the input alignment load-lock can comprise hooks, pins, and thelike. Also, as described above in connection with FIG. 1, the inputalignment load-lock can comprise a conventional input load-lock chamberwith gate valves separating a track from a wafer transport chamber. In alithography system operating at high vacuum, such a wafer transportchamber would be kept at high vacuum while the track would be kept atatmospheric pressure. The input alignment load-lock is thus used totransfer wafers into the high vacuum environment within the lithographyapparatus itself without exposing the entire apparatus to atmosphericpressure.

[0061] In a next step 476, the wafer is aligned with respect to a chuck.As described elsewhere herein, the chuck can be an electrostatic chuck,a vacuum chuck, or a chuck with other mechanical clamping features. In anext step 478, the aligned wafer is secured to the chuck. The securingof the aligned wafer to the chuck can be accomplished by moving thechuck up to and in contact with the wafer and then, in the case of anelectrostatic chuck, charging the electrostatic chuck to thereby securethe wafer to the chuck. Such charging can be accomplished through theuse of pogo contacts on an alignment stage which are in contact withpads on the bottom surface of the electrostatic chuck. Further detailsof steps 476 and 478 are described in greater detail below in connectionwith FIG. 5.

[0062] In a step 480 concurrent with at least one or both of steps 476and 478, a pump-down is performed within the input alignment load-lock.

[0063] In a next step 482, the chuck with the aligned wafer istransported to a lithography patterning chamber. As described above inconnection with FIG. 1, the transportation of the chuck from the inputalignment load-lock to the lithography patterning chamber can beaccomplished by a robot located within a wafer exchange chamber disposedbetween the input alignment load-lock and the lithography patterningchamber. Alternatively, other structures can be used to transport thechuck with aligned wafer from the input alignment load-lock to thelithography patterning chamber, as would apparent to those skilled inthe relevant art(s) given this disclosure. For instance, the chuck andwafer could be placed on a kineumatic mount of the exposure stage.

[0064] Once the chuck with aligned wafer have been placed into thelithography patterning chamber, lithography patterning is performed in anext step 484. Such lithography patterning can include a final alignmentstep as well as additional steps used within lithography patterning asare known to those skilled in the relevant art(s).

[0065] In a next step 486, the chuck with processed wafer are removedfrom the kineumatic mount of the exposure stage to an output alignmentload-lock from the lithography patterning chamber. It should be notedthat the output alignment load-lock is not the same alignment load-lockas the input alignment load-lock. The wafer is only transferred throughthe output alignment load-lock after it has exited the lithographypatterning chamber and needs to be transferred back to track 101. Asdescribed above in connection with step 482, the transportation of thechuck with the processed wafer from the lithography patterning chamberto the output alignment load-lock can be performed with a robot locatedwithin a wafer exchange chamber.

[0066] In a next step 488, the processed wafer is removed from the chuckwithin the output alignment load-lock. This step is substantially thereverse of process step 478, discussed above. Thus, once the chuck withprocessed wafer is transferred to the output alignment load-lock, thechuck can be discharged. Once discharged, the chuck can be lowered awayfrom the wafer leaving the wafer held by the wafer supports.Concurrently with step 488, a venting operation is performed at aconcurrent step 490. As with steps 476, 478, and 480, the venting step480 is performed simultaneously with step 476.

[0067] In a final step 492, the now processed wafer is removed from theoutput alignment load-lock and placed back onto the track.Alternatively, the wafer can be placed onto another structure used tomove wafers away from the lithography apparatus. As would be apparent toa person skilled in the relevant arts, after the final step 492 of themethod 472 of FIG. 4B has been performed, the lithography system hasbeen returned to its condition existing prior to the first step, 474.Accordingly, method 472 can be repeated indefinitely for the lithographypatterning of multiple wafers.

[0068]FIG. 5 is an illustration of a method 500 of aligning a waferwithin an alignment load-lock according to the present invention. In afirst step 510, a wafer is placed on wafer supports. As discussedelsewhere herein, such wafer supports can include hooks, pins, and thelike. Also as discussed elsewhere herein, the wafer can be placed on thewafer supports through the use of a robot or other wafer transportmechanisms, as would be apparent to one skilled in the relevant art(s).

[0069] In a next step 520, the wafer's orientation and location isobserved. Such observation can be conducted, for example, with a cameraand illumination source located outside of the alignment load-lock, asdescribed above in connection with FIG. 2A. The wafer's location isobserved by the camera by analyzing the wafer's radius of curvatureobserved within the camera's field of view. The term location as usedherein in connection with a wafer means the location of the wafer withinan XY plane. Thus, by viewing the radius of curvature of the wafer, thelocation of the center of the wafer can be determined with a patternrecognition unit. Such pattern recognition units and their operation inconnection with a camera and illumination source like the type describedherein are well known to those skilled in the relevant art(s).

[0070] The wafer's particular orientation (i.e. its angular orientationabout its center) is determined by noting the location of a notch withinthe wafer that is also located within the camera's field of view. Inorder to assure that the notch is located within the camera's field ofview upon initial observation, coarse alignment can take place prior tothe method shown in FIG. 5. Such coarse alignment can include, forexample, the use of a wafer spinning module with an edge sensor whichcan be located inside the track. Such a coarse pre-alignment techniqueis known to those skilled in the relevant art(s) and so will not bediscussed more fully herein. While the observation of wafer location andorientation has been described in terms of a single camera, multiplecameras with narrow fields of view can be used to enhance the accuracyof the alignment. By using multiple cameras directed at differentviewpoints along the circumference of the wafer, the location of thecenter and the orientation of the notch can be more precisely determinedthan by using a single camera.

[0071] In a step 525, which can be performed concurrently with step 520,a chuck is moved so as to align the wafer relative to the chuck. Asdescribed elsewhere herein, such a chuck can be an electrostatic chuck,a vacuum chuck, and the like. The chuck is moved relative to the waferthrough the use of an alignment stage like that described in connectionwith FIG. 2B. Movements of the alignment stage are controlled by thesame pattern recognition unit that receives data from the camera used toobserve the wafer. The pattern recognition unit knows the preciselocation of the wafer. The pattern recognition unit also knows theprecise location of the alignment stage by virtue of location feedbackfrom the alignment stage. By direct observation of the chuck with thecamera, the pattern recognition unit can cause the alignment stage tomove the chuck relative to the wafer until the wafer is aligned relativeto the chuck (the diameter of the chuck is purposely a little largerthan the diameter of the wafer).

[0072] Once the chuck and wafer are aligned relative to one another, asubsequent step 530 of placing the chuck in contact with the wafer isperformed. This can be accomplished, for example, by moving the chuckupwards until it is in physical contact with the wafer's bottom surface.As described above in connection with FIG. 2A, the chuck can have, forexample, cutouts to accommodate the wafer supports holding the wafer.Thus, when the chuck is moved upwards into contact with the wafer'sbottom surface, the wafer supports will not interfere with the chuckbecause they are located within the chuck cutouts. Once the chuck isplaced in contact with the wafer, the chuck is secured to the wafer in anext step 540. Securing the chuck to the wafer can be accomplished bycharging the chuck, in the case of an electrostatic chuck.Alternatively, securing the chuck to the wafer can be performed byactivating a vacuum within a vacuum chuck. Other methods of securing thechuck to the wafer can be performed without departing from the scope ofthe present invention.

[0073] Once the wafer has been secured to the chuck in step 540, thechuck can be moved around within a lithography system according to thepresent invention all the while maintaining alignment with the wafer.Since the chuck is equipped with kinematic mounting features, thealignment of the wafer relative to the exposure stage will always bewithin the repeatability of the kinematic mounts used within thelithography system. Typically, the repeatability of such kinematicmounts is within approximately two microns. On the other hand, therepeatability of a robot and gripper is typically a few hundred microns.Therefore, the conventional steps of performing fine alignmentsubsequent to robot movements can be avoided by moving wafers whileattached to chucks. Fine alignment will still be needed. Performing finealignment subsequent to robot movements, however, facilitates the finealignment process. Thus, a lithography system according to the presentinvention, as described above in connection with FIG. 1, can achievehigh levels of throughput, for example 120 wafers per hour, by usingmultiple chucks within the system.

[0074] While the present invention has been described in terms of alithography system working within a vacuum, the present invention couldbe implemented as a non-vacuum system without departing from the scopeof the present invention. In such a system, what has be described aboveas an alignment load-lock could be an alignment and chucking stationwithout the pump-down and venting characteristics of a load-lock.Moreover, a method could be performed according to the present inventionwithout the described pump-down and venting steps.

[0075] Conclusion

[0076] While various embodiments of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. It will be understood bythose skilled in the art that various changes in form and details can bemade therein without departing from the spirit and scope of theinvention as defined in the appended claims. Thus, the breadth and scopeof the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed is:
 1. A lithography system comprising: a lithographypatterning chamber; a wafer exchange chamber coupled to said lithographypatterning chamber; and at least one alignment load-lock separated fromsaid wafer exchange chamber by a second gate valve, said at least onealignment load-lock including an alignment stage that aligns a wafer. 2.The lithography system of claim 1, wherein said wafer exchange chamberis separated from said lithography patterning chamber by a first gatevalve.
 3. The lithography system of claim 1, wherein said alignmentstage aligns said wafer during a pumpdown stage.
 4. The lithographysystem of claim 1, wherein said at least one alignment load-lock is abi-directional alignment load-lock separated from a track by a thirdgate valve.
 5. The lithography system of claim 1, wherein said at leastone alignment load-lock is a unidirectional alignment load-lockseparated from a track by a third gate valve.
 6. The lithography systemof claim 3, wherein said at least one alignment load-lock comprises aplurality of alignment load-locks.
 7. The lithography system of claim 1,wherein said at least one alignment load-lock comprises a first wall anda second wall diametrically opposite from said first wall, wherein saidfirst wall has an opening comprising a motion feedthrough seal thatallows a column to move and prevents the necessity of a rotary seal. 8.The lithography system of claim 7, wherein said second wall has anopening comprising a motion feedthrough seal that allows a column tomove and allows increased stability of the lithography system.
 9. Thelithography system of claim 6, wherein said plurality of alignmentload-locks comprises uni-directional alignment load-locks.
 10. Thelithography system of claim 1, further comprising a spare chuck holdingload-lock separated from said wafer exchange chamber by a third gatevalve.
 11. The lithography system of claim 1, further comprising anillumination source that emits light having an inspection wavelength,and a camera sensitive to said inspection wavelength.
 12. Thelithography system of claim 9, wherein said at least one alignmentload-lock further comprises a load-lock roof transparent to saidinspection wavelength.
 13. The lithography system of claim 1, where insaid at least one alignment load-lock further comprises wafer supportsfor holding a wafer within said at least one alignment load lock. 14.The lithography system of claim 1, wherein said at least one alignmentload-lock further comprises an alignment stage separated from analignment sub-stage disposed outside of said at least one alignmentload-lock by a column extending through a floor of the at least onealignment load-lock.
 15. The lithography system of claim 14, whereinsaid alignment stage includes a plurality of stage engagement mechanismsfor kinematically mounting a chuck.
 16. The lithography system of claim15, wherein said stage engagement mechanisms comprise vee-blocks. 17.The lithography system of claim 14, wherein said floor of the at leastone alignment load-lock includes a motion feedthrough seal that allowssaid column to move relative to said floor while preventing gas flowinto said at least one alignment load-lock.
 18. The lithography systemof claim 17, wherein said motion feedthrough seal comprises elementschosen from the following groups: bellows, elastomer seals, teflonseals, fernofluidic seals and magnetic couplings.
 19. The lithographysystem of claim 1, further comprising at least one chuck.
 20. Thelithography system of claim 19, wherein said at least one chuck is anelectrostatic chuck.
 21. The lithography system of claim 19, whereinsaid at least one chuck is a vacuum chuck.
 22. The lithography system ofclaim 19, wherein said at least one chuck comprises a plurality ofchucks.
 23. The lithography system of claim 19, wherein said at leastone chuck includes a plurality of cut-outs such that said at least onechuck can be brought into contact with a wafer held by a plurality ofwafer supports without contacting said plurality of wafer supports. 24.The lithography system of claim 19, wherein said at least one chuckincludes a plurality of chuck engagement mechanisms on a lower surfacefor kinematically mounting said at least one chuck.
 25. The lithographysystem of claim 24, wherein said chuck engagement mechanisms arehemispheres.
 26. The lithography system of claim 1, wherein saidlithography patterning chamber includes at least one exposure stage thatholds a chuck with a wafer during lithography patterning.
 27. Thelithography system of claim 26, wherein said at least one exposure stagecomprises a plurality of exposure stages.
 28. A method of processing awafer within a lithography system comprising: (a) placing the wafer onsupports within an alignment load-lock; (b) aligning the wafer withrespect to a chuck while the wafer supported within the alignmentload-lock on the supports; (c) securing the wafer to the chuck; and (d)performing a pump-down to create a vacuum within the alignmentload-lock.
 29. The method of claim 28, wherein said step (d) isperformed concurrently with at least one of said steps (b) and (c). 30.The method of claim 28, wherein said step (d) is performed concurrentlywith said step (b) and said step (c).
 31. The method of claim 29,further comprising: (e) transporting the chuck and wafer to alithography patterning chamber; (f) performing lithography patterning onthe wafer; (g) returning the wafer and chuck to the alignment load-lock;(h) removing the chuck from the wafer; and (i) venting the alignmentload-lock.
 32. The method of claim 31, wherein said steps (h) and (i)are performed concurrently.
 33. A method of aligning a wafer within analignment load-lock comprising: (a) placing the wafer on supports withinthe alignment load-lock; (b) observing the location and orientation ofthe wafer on the supports within the alignment load-lock; (c) moving achuck so as to align the wafer with respect to the chuck; (d) placingthe chuck in contact with the wafer; and (e) securing the wafer to thechuck.
 34. The method of claim 33, wherein said step (b) furthercomprises observing the location and orientation of the wafer on thesupports within the alignment load-lock with a camera located outside ofthe alignment load-lock.
 35. The method of claim 33, wherein said step(d) further comprises moving the chuck upwards until it lifts the waferup off of the supports.
 36. The method of claim 33, wherein the chuck isan electrostatic chuck, and said step (e) further comprises charging theelectrostatic chuck.
 37. A lithography system comprising: a lithographypatterning chamber; a wafer exchange chamber adjacent to saidlithography patterning chamber; at least one alignment chucking stationadjacent to said wafer exchange chamber; and a plurality of chucks;wherein wafers are moved to and from the lithography patterning chamberwhile being affixed to respective ones of said plurality of chucks.